Literary foreshadowing suggests upcoming events to the reader. Word choice, events and descriptions may all create foreshadowing. For instance, a description of a happy picnic scene in a bright meadow contrasted with dark clouds building on the horizon creates a sense of impending doom, so readers might expect something to go terribly wrong at the picnic. An example from literature occurs in Shakespeare's Romeo and Juliet where the prologue announces that "A pair of star-cross'd lovers take their life."
Foreshadowing may be more subtle than Shakespeare's play, however. For example, the way characters act and react in Shirley Jackson's "The Lottery" foreshadow the negative end for the main character. A tone of solemnity pervades the situation with descriptions like "[The men] stood together, away from the pile of rocks in the corner, and their jokes were quiet," helping the reader sense the seriousness. Writers sometimes use reader's expectations to leave false clues about future events, termed "red herrings," to help make a twist ending more surprising.
Masterfully used foreshadowing builds the dramatic tension in a text. Even though readers may "know" what is going to happen due to foreshadowing, the knowledge does not ruin the story. For example, when Lenny accidentally kills the puppy in John Steinbeck's "Of Mice and Men," readers likely believe a person will fall victim to Lenny's combination of physical strength and low IQ, but exactly who, when, how and what the outcome will be remain a mystery.
Foreshadowing also helps prevent confusion and makes it more likely readers will believe fantastic events that occur in the story if they prepare for such events. The reluctance of the characters in the movie "Signs" to believe in an alien invasion helps audiences buy into the fact that they might be real. In the same movie, without the information about the son's asthma, his survival of the alien attack seems confusing. Foreshadowing helps prepare readers for outlandish occurrences in a story.